The invention relates to a method and construction of a reflector for wide angle observation of a reflecting surface via a reflex sensor which may also be equipped with polarization filters, or can operate as a laser reflex sensor.
The wide-angle sensor system with a cube corner surface comprises a gauge for selecting the observation angle. The cube corner surface comprises a multiplicity of cube corners. The cube corner part surfaces arranged around the center of the cube corner, specifically its reflecting sides, are at right angles to one another. The axis of the cube corners deviate alternately by −5° and +5° or more from the axis normal to the reflector surface. The surface of at least one cube corner surface is lengthened substantially.
The aim of the wide-angle sensor system with a cube corner part surface is to create a reflex sensor system wherein it is possible to observe a surface with an aperture angle of approximately 80° and more in conjunction with a retro-reflective value at each angle of illumination of the observed horizontal surface of at least 3000 mcd/lx.
Moreover, this system can be used to observe moving bodies in space, for example vehicles or transport gondolas, even if these bodies are changing their angle relative to the observer. For example, a conveyor gondola can be viewed when being guided in a curve. A connected measuring system, for example for measuring distance or position, can operate reliably, only because the intensity of a reflection signal from the body to be observed is always received at a strong enough level of at least 3,000 mcd/lx.
The problem is that there have not been any qualitatively satisfactory reflecting surfaces which continuously supply an intensive retro-reflection signal available on the market for the tasks of reflex sensor technology. This is particularly true when the reflecting surface is positioned deviating at 40° or more from the normal to the reflection signal. The retro-reflectors or reflecting films on the market having wide angled properties are conceived for road traffic, for reflecting sign boards or retro-reflectors for personal protection on clothes. These reflecting structures produce a wideband distribution of the reflected light. It follows that their reflected light energy is insufficient to provide reflex sensors with focused reliable retro-reflection signals. For reflex sensors, there is a need for as large as possible portion of the light to be retro-reflected on target to the receiver.
Only with constant, high retro-reflective power is it possible to have a signal read by a sensor having an additional polarization filter system which consumes half to two-thirds of the transmitted light. This energy is no longer available to the receiver of the sensor for the purpose of further interpretation. The polarization filter system serves chiefly to distinguish the light emitted by the sensor. It is then rotated in polarity and retro-reflected by the retro-reflector from extraneous light or reflections which can emanate from other bodies in space. The wide-angle system according to the invention with its cube corner reflector of specific design, permits the operation of the sensor with a polarization filter system.
Moreover, this novel cube corner reflector can also be constructed, using known technology, as a microcube reflector, as is required, for laser sensor technology or film technology. The requirements for laser sensor technology are described for this purpose by the inventor in German Patent DE 197 27 527 incorporated herein by reference. The point is that pyramidal cube corner surfaces are completely unsuitable for the stated aim of the present invention. This is because they retro-reflect only approximately 66% of the light, and that they are unsuitable for the required light beam contour and precision for laser sensors. The invention therefore utilizes a specific configuration of full-cube cube corners.
Full-cube corners whose cube corner axis deviates from the axis normal to the reflector, are familiar in production in retroreflector technology.
The cubic, reflecting mirror system known in metrology as the Perkin-Elmer pyramid is known to the prior art and is currently designated as full cube in the case of retroreflectors. A full-cube cube corner consists of three square mirrors which are at right angles to one another and retroreflect the light to the light source. Stimson describes in Great Britain Patent GB-B 269 760 incorporated herein by reference, a series of molds which produce the cubic, reflecting surfaces by using individual ground pins or notched plates.
Gubela describes in German Disclosure Reference DE 44 10 994, incorporated herein by reference, bodies and/or components of a billet-shaped cube corner reflector and/or mold element for molding cube corner reflectors with full cube properties. These billet-shaped components can be assembled to form surfaces with particular ease in micro-structure technology and constitute a production technology which is also suitable for producing molded parts or presenting the reflector according to the invention with wide angle properties for the sensor tasks.
The reflector described in the present invention, and the production of the molds, are based on the known methods for producing cube corner reflectors, but select a novel shape, which comes close to but differs from the full cube.
There are also other cube corner shapes such as the three-faced pyramid. However, the preferred design is that of a variation of the full cube, since it basically has a substantially lower scattering loss than the pyramid. Pyramidal cube corner structures can be cut from a flat common surface, whereas full-cube cube corners require the arrangement of a multiplicity of components in the mold construction to represent large structured surfaces of a multiplicity of cube corners. The manufacturing methods and their advantages and disadvantages in the production of cube corners are known to the person skilled in the art and need not be repeated here.
The invention makes use of the presence and use of full-cube cube corners in technology. The full-cube cube corner has the excellent property of receiving incident light over a wide tolerance range of the incidence angle, and retro-reflecting it substantially completely to the light source. The retro-reflection is performed via the reflection of light at the three square surfaces of the full-cube cube corner. This angular tolerance for the incident light is currently being used in practical application in the case of most reflection light barriers. The mounting and alignment of the retro-reflector at the correct angle to the transmitter/receiver system is simple and fault-tolerant. Vibration-induced beam movements are also mostly tolerated by this reflective element with full-cube cube corners.
When using laser light sensors, the application of cube corners as reflective element becomes very difficult. This is because in inexpert application, the laser supplies information relating to its movement on the retro-reflection structure and information relating to the shape of the retro-reflection structure, instead of information relating to the space to be observed between the transmitter/receiver and retro-reflecting mirror. German Reference DE 197 27 527 shows how retro-reflecting mirrors must be shaped for laser sensors, and also explains the differences between full-cube and pyramidal cube corners and teaches which shape the laser sensor beam must have. As a result of applying the known teaching, the advantages of the structure composed of full-cube cube corners are also obtained with laser sensors in the case of the present invention. It is likewise possible to use the inventive reflector of the wide-angle sensor system.
The text below further discusses only cube-corner systems which can be assigned to the full cube. It is necessary to distinguish in the case of cube corners between the pyramidal cube corners, which can be cut from a base surface, and full-cube cube corners which, by contrast, can be produced only by assembling subsegments.
Regarding the Perkin-Elmer pyramid, the part surfaces of the cube corners are square, the inventive wide-angle sensor system uses as cube corner reflector a specific variation of the full-cube cube corner. In this case, at least one cube corner surface is substantially larger than the smallest cube corner part surface.
This enlarged, lengthened cube corner part surface assists in collecting light incident even from a very wide angle, and in passing it on to the remaining cube corner part surfaces such that the light is retro-reflected in the direction of the light source. The result is a cube corner which operates in practice in a substantially wider angled manner than in previous designs.
By contrast, in the case of retro-reflectors for motor vehicles, for example, reflecting surfaces acting over a wide angle are represented by cambering the entire reflector. The reflector surface is formed from a multiplicity of individual reflecting pins which look in the desired directions, such that a plastic wide angle reflector that can then be molded by means of electrochemical forming. The cube corners produced in this case always have virtually square cube corner part surfaces of the same size. The wide-angle nature of the reflector produced is then based only on the fact that cube corners with differently aligned cube corner axes have been combined. Depending on the incidence angle of the light, there is always only a very small portion of the cube corners working, whose axes look in the direction of the light. Thus with this design, the retro-reflective power is accordingly very low.
Manufacturing methods have been selected for the reflector of the present invention which produce a specific cube corner surface whose character differs plainly from reflecting surfaces which have been formed by pins. In the case of full-cube reflectors, which are represented by pins, the cube corner part surfaces are approximately of the same size and square. At least one cube corner part surface is substantially larger per cube corner than the smallest cube corner part surface of the cube corner in the case of the specific variation of the full-cube cube corner as it is used in the reflector according to the invention. The substantially enlarged, specifically lengthened cube corner part surface permits light incident from a very wide angle to be collected, and allows for excellent retro-reflective values (see FIGS. 32 and 33).
Some of the drawings and illustrations of this description of the invention resemble disclosure document DE 101 19 671 of the same inventor, which is incorporated herein by reference. The similarity is based on the similarity of the production techniques used for the cube corner shapes.
The specific cube corner shape according to the invention with an enlarged, lengthened cube corner part surface is achieved by presenting the cube corners using the plate method, which is described by Stimson in British Patent GB-B 269 760. Of course, in departure therefrom, modern manufacturing techniques are used as well as materials of microstructure technology. However, the inventive structure of the reflector deviates clearly from Stimson. The cube corner is cut in alignment with the axis which is normal to the reflective surface, in the case of the inventive reflector, the cube corner axes of the cube corners are aligned so that they deviate strongly from the normal to the reflector surface, specifically at least +/−5°. This alignment is in a manner combined with cube corners whose cube corner axes deviate, for example, +/−15° from the axis normal to the reflector surface.
The desired lengthened cube corner part surface is produced by notching the mold element plates upon application of the Stimson plate method by the oblique wedge-shaped incision in the plates.
A cube corner part surface which is still likewise long, but by contrast virtually unbounded in width, is obtained upon using the plate method as it has been described by Gubela in German Patent Application DE 44 10 994 C2, incorporated herein by reference for example in FIGS. 13 and 14 in that application.
In the Gubela method, an alignment of the cube corner axes of 5° deviating from the axis normal to the reflector surface, is very advantageous for the inventive wide-angle sensor system. After all, when the reflector is presented with the aid of this method, a wide-angle property is additionally obtained not only in the horizontal direction, but also in the vertical direction.